The formation of oligomers of amyloid-beta is one of the critical factors in the development of Alzheimer's disease, according to the Amyloid Cascade Hypothesis. Drugs that can effectively inhibit A2 production and thus reduce the amount of aggregation would benefit millions of patients world-wide. Ultimately, accessing novel chemical diversity, which complements existing screening libraries, may be the key to unlocking these treatments. Our long-term goal therefore is to discover new drug-like small molecules from marine sources that can be used for the treatment of Alzheimer's disease or as biochemical probes to further our under- standing of the development of this disorder. The objective of this proposal, which is our next step in pursuit of that goal, is to identify these lead compounds using a new screening protocol that will rapidly link a spe- cific compound in a mixture to the observed biological effect without requiring laborious bioassay guided isolation (Aim 1). Rigorous biological evaluation of the inhibitors will identify the best lead (Aim 2). This pro- posal is innovative because it addresses the fundamental barrier in natural products of how to link chemical structure to activity in a new way and applies this solution to the problem of Alzheimer's drug discovery. The specific aims of the proposal are: 1. To identify inhibitors of 2-secretase (BACE1) using an innovative protocol that rapidly links a specific compound within a mixture to the observed biological activity using a new LC-MS homogenous affinity assay. 2. To evaluate the potential of the new inhibitors as BACE1 leads using a gauntlet of assays designed to identify the best candidate. We expect to identify structurally unprecedented classes of BACE1 inhibitors. These new classes of poten- tial anti-Alzheimer drug leads will be evaluated in a series of biochemical assays to assess parameters criti- cal to CNS drug development. A limited number of compounds that meet these requirements will be ad- vanced to further studies in partnership with industry. If successful, the newly discovered leads are ex- pected to have a positive impact by finally validating BACE1 as a drug target, validating the Amyloid Cas- cade Hypothesis and providing desperately needed therapeutics for Alzheimer's patients.